8,184 research outputs found
Reduced Density Matrix Approach to Phononic Dissipation in Friction
Understanding mechanisms for energy dissipation from nanoparticles in contact
with large samples is a central problem in describing friction microscopically.
Calculation of the reduced density matrix appears to be the most suitable metho
to study such systems that are coupled to a large environment. In this paper
the time evolution of the reduced density matrix has been evaluated for an
arbitrary system coupled to a heat reservoir. The formalism is then applied to
study the vibrational relaxation following the stick-slip motion of a small
adsorbate on a surface. The frequency dependence of the relaxation time is also
determined.Comment: 16 pages, 3 figures (included), revte
Memory Card
âI have always had a phenomenal memory,â a sentiment that I just recently remembered. Growing up I could recite every number in a thirteen string, remember a poem after one read, quote every menial conversation I had ever had. I considered myself cursed and blessed with an elephantâs memory: it made me extremely sensitive to others, often confused and upset when I heard people repeat the same things to me and make the same gestures. Had our interaction not meant anything? Do they not remember me?
Now I donât remember. I lose things. I feel irresponsible with objects and conversations and parts of my life. The funny part about remembering your memory is that it means youâve forgotten it. What kind of a memory is that?
After tackling mountains of old home videos, revisiting birthday cards, story books, terrible essays from high school, my project was conceived: an attempt to reevaluate and reconstruct older memories in my life. At the start of the process I only looked at the past, until I realized â why stop there?
In the frame of a found memory card the viewer scrolls through small moments of my childhood, things I can remember, until reaching a point in which it glitches â in which the viewer cannot tell the difference between reality and fantasies of events, as well as the environment they exist in. Past this point, old memories are recreated and explored, lead by a fictionalized older version of myself. However, there is a catch: none of my memories that take place in the future have happened yet.
Through the body of a memory card and the small story of a woman who breaks the screen to talk to you, I am curating parts of my past and parts of my future.
I donât intend the piece to seem explicitly about myself, instead, a character that exists within the memory card. She jumps between multiple ages throughout the piece, and wanders aimlessly through her own environments, describing events that happened while leading the viewer through worlds that only become more visually distressed; the piece is intended to age and become confused in narrative as memory does over time. She encounters many visual glitches, pauses, and errors in her world, as she is also grappling with her own relationship to the digital media and film that has captured her, as well as memoryâs relationship to error as it accumulates and is stored in the mind.
In her world things do not make sense, though the environments exist as fully as any would. With time and exploration colors prevail over specifics, and we find ourselves riding a boisterous wave of sound and place. Where to? Where does it all lead? Well, I promise Iâll let you know when I remember
Unbounded Human Learning: Optimal Scheduling for Spaced Repetition
In the study of human learning, there is broad evidence that our ability to
retain information improves with repeated exposure and decays with delay since
last exposure. This plays a crucial role in the design of educational software,
leading to a trade-off between teaching new material and reviewing what has
already been taught. A common way to balance this trade-off is spaced
repetition, which uses periodic review of content to improve long-term
retention. Though spaced repetition is widely used in practice, e.g., in
electronic flashcard software, there is little formal understanding of the
design of these systems. Our paper addresses this gap in three ways. First, we
mine log data from spaced repetition software to establish the functional
dependence of retention on reinforcement and delay. Second, we use this memory
model to develop a stochastic model for spaced repetition systems. We propose a
queueing network model of the Leitner system for reviewing flashcards, along
with a heuristic approximation that admits a tractable optimization problem for
review scheduling. Finally, we empirically evaluate our queueing model through
a Mechanical Turk experiment, verifying a key qualitative prediction of our
model: the existence of a sharp phase transition in learning outcomes upon
increasing the rate of new item introductions.Comment: Accepted to the ACM SIGKDD Conference on Knowledge Discovery and Data
Mining 201
Neutrino-induced coherent pion production off nuclei reexamined
It is pointed out that so far all theoretical estimates of coherent pion
production off nuclei induced by neutrinos rely on the 'local approximation'
well known in photonuclear physics. The effects of dropping this approximation
are discussed. It is found that in a plane wave approximation for the pion the
local approximation overestimates the coherent neutrino-induced pion production
on nuclei.Comment: v3: comments on pion FSI added, minor corrections; version as
published in Phys. Rev.
Mol. Cell. Proteomics
Chemical cross-linking in combination with mass spectrometric analysis offers the potential to obtain low-resolution structural information from proteins and protein complexes. Identification of peptides connected by a cross-link provides direct evidence for the physical interaction of amino acid side chains, information that can be used for computational modeling purposes. Despite impressive advances that were made in recent years, the number of experimentally observed cross-links still falls below the number of possible contacts of cross-linkable side chains within the span of the cross-linker. Here, we propose two complementary experimental strategies to expand cross-linking data sets. First, enrichment of cross-linked peptides by size exclusion chromatography selects cross-linked peptides based on their higher molecular mass, thereby depleting the majority of unmodified peptides present in proteolytic digests of cross-linked samples. Second, we demonstrate that the use of proteases in addition to trypsin, such as Asp-N, can additionally boost the number of observable cross-linking sites. The benefits of both SEC enrichment and multiprotease digests are demonstrated on a set of model proteins and the improved workflow is applied to the characterization of the 20S proteasome from rabbit and Schizosaccharomyces pombe
A Turbulent Origin for Flocculent Spiral Structure in Galaxies: II. Observations and Models of M33
Fourier transform power spectra of azimuthal scans of the optical structure
of M33 are evaluated for B, V, and R passbands and fit to fractal models of
continuum emission with superposed star formation. Power spectra are also
determined for Halpha. The best models have intrinsic power spectra with 1D
slopes of around -0.7pm0.7, significantly shallower than the Kolmogorov
spectrum (slope =-1.7) but steeper than pure noise (slope=0). A fit to the
power spectrum of the flocculent galaxy NGC 5055 gives a steeper slope of
around -1.5pm0.2, which could be from turbulence. Both cases model the optical
light as a superposition of continuous and point-like stellar sources that
follow an underlying fractal pattern. Foreground bright stars are clipped in
the images, but they are so prominent in M33 that even their residual affects
the power spectrum, making it shallower than what is intrinsic to the galaxy. A
model consisting of random foreground stars added to the best model of NGC 5055
fits the observed power spectrum of M33 as well as the shallower intrinsic
power spectrum that was made without foreground stars. Thus the optical
structure in M33 could result from turbulence too.Comment: accepted by ApJ, 13 pages, 10 figure
Fatigue Strength of HFMI-treated High-strength Steel Joints under Constant and Variable Amplitude Block Loading
AbstractLightweight-design of welded high-strength steel structures in cyclic service necessitates the use of post-treatment methods like the high frequency mechanical impact treatment (HFMI). Service loads during operation mostly consist of variable amplitudes, whereat recommendations are only available for the as-welded condition. Therefore, this paper deals with the effect of variable amplitude block loading on the fatigue strength of HFMI-treated T-joints. An evaluation of the real damage sum exhibits characteristic distinctions to constant amplitude test results in regard to the base material strength. The application of an equivalent stress range method by nominal and effective notch stress approach is finally presented
Health-Related Quality of Life Associated With Pain Health States in Spinal Cord Stimulation for Chronic Neuropathic Pain.
OBJECTIVES:A substantial proportion of patients have recently reported pain reduction levels of â„80% following treatment with Evoked Compound Action Potential (ECAP) spinal cord stimulation (SCS). The additional health-related quality of life (HRQoL) utility gain that can be achieved in this patient group is unclear. The aim of this study is to quantify the HRQoL utility values seen in a remission health state (defined as â„80% pain reduction) and contrast with more traditional health states of <50% and â„50% pain relief. MATERIALS AND METHODS:Pain intensity assessed using a 100âmm visual analogue scale (VAS) and EQ-5D-5L questionnaires were collected from 204 patients treated with ECAP SCS for chronic back and leg pain and followed up to 12âmonths. Utility values were derived using EQ-5D-5L responses crosswalked to EQ-5D-3L. Linear regression models adjusted for baseline utility values and patient demographics were used to compare differences in utility values across health states. RESULTS:Patients in the remission health state (i.e., â„80% pain reduction) consistently reported statistically significant greater utility values (+0.09 to +0.15, all pâ<â0.003) compared to patients reporting â„50% pain relief at 3- and 12-month follow-up for overall, back, and leg VAS pain. The gain in utility values per percent unit of pain reduction was statistically significant at 3- and 12-month follow-up with a mean increase in HRQoL utility score between 0.003 and 0.005 observed for each percent of pain reduction. CONCLUSION:Our analyses show that patients in a remission health state report statistically and clinically significant better HRQoL than patients experiencing lesser pain relief
Discrete breathers in polyethylene chain
The existence of discrete breathers (DBs), or intrinsic localized modes
(localized periodic oscillations of transzigzag) is shown. In the localization
region periodic contraction-extension of valence C-C bonds occurs which is
accompanied by decrease-increase of valence angles. It is shown that the
breathers present in thermalized chain and their contribution dependent on
temperature has been revealed.Comment: 5 pages, 6 figure
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